1. Field of the Invention
The present invention relates to an acoustic paper diaphragm and an acoustic transducer apparatus including the acoustic paper diaphragm, that is, mainly a loudspeaker.
2. Description of the Related Art
Paper diaphragms made from pulp by means of a papermaking method (a method of making a sheet of paper) are typically used as acoustic diaphragms provided in acoustic transducer apparatuses such as loudspeakers. With moisture-absorption characteristics, paper absorbs moisture depending on the moisture condition of the environment in which the paper is used, which greatly affects Young's modulus, strength and the like that are important to acoustic diaphragms. In order to minimize this effect, treatment called “sizing” is applied to paper diaphragms and moisture resistance is improved.
Sizing treatment is practically classified into two kinds, that is, internal addition and external addition and generally classified as shown in FIGS. 3A and 3B. Internal addition is the sizing treatment executed when making a sheet of paper as shown in FIG. 3A. External addition is, as shown in FIG. 3B, the sizing treatment in which a sizing agent is applied to paper after it is made, or in which paper is impregnated with a sizing agent after it is made. Internal addition is the treatment in which a sizing agent exists inside paper layers, and part of which is made to be exposed on the surface. On the contrary, external addition is the treatment in which a sizing agent is not contained much inside paper layers but is made to cover the surface.
As a sizing agent used for internal addition, what is called “latex” in which particles of natural rubber or synthetic rubber are dispersed in water is often used. Other than latex, a number of materials such as transformed natural resin (pine resin) and the one made from synthetic macromolecules are used as sizing agents. In the internally-adding sizing treatment in a general papermaking method, after a sizing agent is added to and dispersed in what is called pulp slurry in which pulp that is raw material for paper is dispersed in water in advance, an aluminum sulfate (Al2(SO4)318H2O) solution is added as a sizing-agent fixing agent to fix the sizing agent on the surface of pulp fiber. Paper is obtained by making this pulp slurry into a sheet. Sizing effectiveness such as improvement in properties (strength and so on) and moisture resistance can be obtained in a drying process when making a sheet of paper, where a sizing agent is melted to cover the pulp surface or to disperse on the surface.
In the externally-adding sizing treatment, a sizing agent is applied to or impregnated into a sheet of paper. As a sizing agent, natural resin, nitrocellulose or cellulose acetate into which cellulose has been transformed, or a synthetic macromolecular material is used after liquidized and emulsified.
Acoustic paper diaphragms are described in Patent documents 1 and 2. In Patent document 1, an acoustic paper diaphragm formed of cone paper coated with a layer containing bacterial cellulose is described. In Patent document 2, an acoustic paper diaphragm formed of a sheet including a compound containing glass particles and polyamide resin is described.
[Patent Document 1] Published Japanese Patent Application No. H9-84175
[Patent Document 2] Published Japanese Patent Application No. 2001-298791